The most commonly known and widely used type of circuit board assembly comprises an insulating circuit board having electrical components mounted on a first surface thereof and having conductors on the second or oppositely facing surface of the board. Holes are provided in the board for the leads which extend from the components, when the board is manufactured, the components are assembled to the first surface so that the leads extend through the holes in the board. The ends of the leads are then soldered to the conductors on the second surface of the board. The manufacturing process by means of which such boards are produced is very forgiving in the sense that the lengths of the leads extending from the components are not critical but can vary within fairly wide limits. Furthermore, the fact that the leads extend through holes in the board provides a strain relief for the solder connections on the second surface of the board between the ends of the leads and the circuit board conductors. In other words, if the component from which the leads extend is handled by a technician, the handling of the component and the circuit board will not cause stresses which might be transmitted to the soldered connections and which might disturb these connections.
There is a trend away from the types of circuit boards discussed above and towards the use of circuit boards having both the circuit board conductors and the components on the first surface of the circuit board. The term "surface mounting" has been adopted to describe the techniques for securing and mounting components on the surface of a circuit board on which the conductors are provided and standard procedures are being developed for carrying out the assembly, mounting and solder operations.
In general, a circuit board having surface mounted components thereon is produced by metallizing the first surface of the board in those locations where the conductors are required and silk screening a solder paste on the metallized portions. The solder paste is a viscous material which, when heated, is capable of fusing and forming a solder joint. The components can be assembled to the board by simply aligning the leads extending from the components with the conductors on the board and lowering the component onto the board. Soldering is carried out by passing the board through a heating medium sufficient to cause fusion of the solder.
In the finished circuit board, the leads extending from the components simply rest on the circuit board conductors and are held on the board solely by the solder which has been fused onto the leads and the circuit board conductors. The solder, therefore, is required to serve as both a mechanical fastening and as an electrical connection. Since the conductors are quite narrow, the area of the solder joints is quite small and the joints are not very strong.
The mounting of devices which are not handled or which are not subject to stresses or strains presents no significant problems for surface mounting manufacturing methods. After a chip carrier or a transistor, for example, is mounted on a circuit board, it is virtually never touched by human hands and it is not subjected to stresses or strains other than those imposed by its own mass. The solder joints between the leads of the chip carrier or the like and the circuit board conductors are sufficient to hold the device in its position on the circuit board. However, there are other devices which are mounted on the circuit board which must be handled and which must withstand the imposition of forces from an external source. Such devices might be, for example, switches having parts which are turned or rotated when the switch condition is changed, rheostats, and electrial connector receptacles designed to receive a complimentary connector plug. Every time the plug is inserted into, or extracted from, the receptacle, forces are imposed on the connector housing and these forces will inevitably be transmitted to the solder joints unless precautions are taken to prevent such transfer.
The present invention is directed to the achievement of a solution to the problems of mounting devices by surface mounting techniques on circuit boards which devices are subject to external forces and which must be capable of withstanding stresses imposed by external forces. The invention is discussed generally with reference to an electrical connector receptacle, however, the principles of the invention can be used for other surface mounted circuit devices.